Combustion chambers form part of gas turbines, which are used in many fields for driving generators or machines. In such applications the energy content of a fuel is used to generate a rotational movement of a turbine shaft. For this purpose the fuel is combusted by burners in the combustion chambers connected downstream thereof, with compressed air being supplied by an air compressor. As a result of the combustion of the fuel a highly pressurized working medium is produced at a high temperature. Said working medium is directed into a turbine unit connected downstream of the combustion chambers, where it expands in a manner that delivers work output.
In this arrangement a separate combustion chamber can be assigned to each burner, whereby the working medium flowing out of the combustion chambers can be combined before or in the turbine unit. Alternatively, however, the combustion chamber can also be implemented in what is known as an annular combustion chamber design, in which a majority, in particular all, of the burners open out into a common, typically annular, combustion chamber.
In addition to the attainable output power, one of the design goals in the design of gas turbines of said kind is a particularly high level of efficiency. In this case an increase in efficiency can basically be achieved for thermodynamic reasons through an increase in the exit temperature at which the working medium flows out of the combustion chamber and into the turbine unit. For this reason temperatures of around 1200° C. to 1500° C. are aimed at and also achieved for gas turbines of said kind.
With the working medium reaching such high temperatures, however, the components and parts exposed to this medium are subject to high thermal stresses. In order nonetheless to ensure a comparatively long useful life for the affected components while maintaining high reliability, it is usually necessary for said components, in particular the combustion chamber, to be constructed of particularly heat-resistant materials and for a means of cooling them to be provided. In order to prevent thermal deformations of the material which limit the useful life of the components, efforts are usually made to achieve as uniform a cooling of the components as possible.
For this purpose the combustion chamber wall is typically lined on its inside with heat shield elements which can be provided with particularly heat-resistant protective layers and which are cooled through the actual combustion chamber wall. Toward that end, a cooling method also known as “impingement cooling” can be employed. With impingement cooling a cooling medium, generally cooling air, is supplied to the heat shield elements through a plurality of holes drilled in the combustion chamber wall so that the cooling medium impinges essentially vertically onto its cooling surface formed on the cold side and facing the combustion chamber wall. The cooling medium heated up by the cooling process, e.g. cooling air, is subsequently discharged from the inner space that the combustion chamber wall forms with the heat shield elements. A further cooling process in which a longitudinal backflow of the heat shield elements along a cooling surface facing the combustion chamber wall is used, is the technique known as convective cooling.